In the course of production of light sources of the above-mentioned character the productivity of the pumping technology employed is determined by the volume of the discharge vessel and the duration of pumping required for dissociating the carbonates at the cathodes.
According to a known, currently used process a rapid exhaustion of the discharge space to a very high quality is achieved by pumping from both ends and by a reduction of the flow resistance. In order to be able to achieve the aim set, at both sides exhaust tubes of minimum length are used or exhaust tubes are not utilised at all. Flushing gas is introduced in several stages into the discharge vessel and pumping out takes place at both ends of the light tube simultaneously.
A disadvantage of this process consists in that the space and energy requirements are very high as a consequence of the required pumping output. Because of the pumping taking place at both sides problems are involved in the dismantling of the vacuum gas system connected to one of the exhaust tubes, with regard to the purity of the vacuum.
In German Federal Republic patent No. 30 03 700 a process for pumping out discharge vessels is described wherein gas is introduced only through one of the exhaust tubes of a discharge vessel while at the other exhaust tube only pumping out occurs, and in the course of which in the first phase of the pumping a discharge vessel is pumped out to a pumping pressure value which is higher than the charge pressure of a discharge vessel, whereafter flushing gas is introduced into the interior of the discharge vessel via the pumping tube on the gas side, and this gas is pumped out via the other exhaust tube while simultaneously maintaining the pumping pressure value. Flushing through is undertaken at a predetermined gas velocity during a certain time period; during this also the carbonates are dissociated to oxides at the cathodes. In the next phase of the pumping ot the gas pressure prevailing in the discharge vessel is reduced to the charging pressure corresponding to the type of the discharge vessel and moreover in such a manner that the gas supply is first blocked and after attaining the charging pressure, the pumping is terminated and the exhaust tubes at both sides are tipped off (sealed).
A disadvantage of this solution is that the gas flushing undertaken at a high pressure value causes the consumption of much excess gas which significantly increases the costs of the process. Furthermore the adjustment of the charging pressure with the required accuracy is rather complicated, which can be traced back to the dimensional tolerances of the exhaust tube at the suction side and which in turn causes a significant change in the flow velocity.
A further drawback lies in that the time required for the pumping process is too long as a consequence of the adjustment of the pressure to the charge pressure.